1. Field of the Invention
The present invention relates to a method of preventing corrosion of a titanium layer in a semiconductor wafer.
2. Description of the Prior Art
A dielectric layer is normally positioned between the MOS (Metal Oxide Semiconductor) transistor and each of the metal conducting wire in a semiconductor wafer for separating and protecting the components in the semiconductor wafer. In order to successfully connect these components in the MOS to each of the metal conducting wire so as to form a complete electronic device, a contact plug formed in the dielectric layer is necessary to be used as a conducting wire between the MOS and each corresponding metal conducting wire. Therefore, just how to upgrade the quality of process for manufacturing the contact plug and the metal wire layer has become an important subject matter in the study of the process for manufacturing the semiconductor.
Please refer to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are the prior art's schematic diagrams of the manufacturing process of the contact plug 24 of the semiconductor wafer 10. The semiconductor wafer 10 comprises a bottom conducting layer 12 and a dielectric layer 14 positioned at the top of the bottom conducting layer 12. As shown in FIG. 1, conventional process for manufacturing the contact plug 24 is first to perform photolithography and etching processes in order to form a contact hole 16, then to deposit in sequence, on the surfaces of the semiconductor wafer 10 and the contact hole 16, a titanium layer 18, a TiN (titanium nitride) layer 20, and a conducting layer 22 composed of tungsten. Thereafter, as shown in FIG. 2, by the use of CMP(Chemical Mechanical Polishing)process to perform a surface treatment on the semiconductor wafer 10 to uniformly remove the conducting layer 22, the TiN layer 20, and the titanium layer 18 on the surface of the dielectric layer 14 in order to form a contact plug 24, and in the mean time, to cut the top of the contact plug 24 to be at the same level as that of the dielectric layer 14.
Please refer to FIG. 3 and FIG. 4. FIG. 3 and FIG. 4 are the prior art's schematic diagrams of the manufacturing process of the metal wire 40 of the semiconductor wafer 10. After completing the fabrication process of the contact plug 24, a normal metallization process continues to manufacture the metal wire 40 such that the bottom conducting layer 12 connects to the other components in the semiconductor wafer 10 through the contact plug 24 and the metal wire 40 to gradually form a complete circuit. The conventional way of fabricating the metal wire 40 is first to uniformly deposit, on the surface of the dielectric layer 14 and the top of the contact plug 24, a titanium layer 26 and a protecting layer 28 composed of TiN, it then to form in sequence, on the protecting layer 28, an aluminum conducting layer 30 and an anti-reflective coating layer 32 composed of TiN, in the mean time, to define and form the pattern of metal wire 40 by the use of the photolithography and etching processes.
As shown in FIG. 4, while fabricating the metal wire 40, misalignment of the metal wire 40 often occurs due to the limitation of the manufacturing techniques or other factors, that is to say, the patterned photoresist layer 34 used for defining the metal wire 40 is unable to completely cover right at the top of the contact plug 24 even though there is a certain tolerance range in this metal misalignment phenomenon, in other words, only a portion of the metal wire 40 covers on top of the contact plug 24.
Since only a portion of the metal wire 40 covers on top of the contact plug 24, a portion of the conducting layer 22 and titanium layer 26 will be exposed on the surface of the semiconductor wafer 10. And since the tungsten's chemical potential is higher than that of the titanium, the titanium layer 26 on the titanium-tungsten interface 38 is subject to be corroded by the photoresist stripper solution during the upcoming photoresist stripping process of the photoresist layer 34. As a result, the corrosion situation will decrease the contact area between the metal wire 40 and the contact plug 24 and increase the resistance of the contact plug 24 or increase the contact resistance between the contact plug 24 and the metal wire 40, or it will even cause a serious result of disconnection of the circuit.